Sulfur dioxide and oxygen in the mole ratio 2:1 were mixed at a
constant temperature of 1110K and a constant pressure of 9atm in
the presence of a catalyst. At equilibrium, one-third of the sulfur
dioxide had been converted into sulfur trioxide. Calculate the
equilibrium constant Kp for this reaction under these
conditions.
Since moles and partial pressures are directly proportional (when
temperature and volume remain constant), hence Initial partial
pressures of SO2, O2 and SO3 are (2/3)(9)atm, (1/3)(9)atm
and 0 atm respectively.
Since at equilibrium, one-third of the sulfur dioxide had been
converted into sulfur trioxide, Change will be -(1/3)(2/3)(9)atm
for sulfur dioxide and applying stoichiometry you can determine the
corresponding partial pressure Changes for oxygen and sulfur
trioxide.
Accordingly, you can determine the Equilibrium partial pressures
for all 3 species, and consequently the Kp value.